Known from Published International Patent Application, WO A 02/060805 is a measuring system for measuring at least one measured variable in such case, a mass flow rate, a total mass flow, a volume flow rate, or a volume flow of a flowing fluid, for example, a liquid or a gas. This measuring system serves, especially, as a transfer location for a fluid product, for example, a petroleum, a liquid fuel, a liquefied gas or the like, and is formed by means of a fluid supply line connected to a supply container, for example, a tank, containing fluid, by means of a fluid return line connected to the supply container, by means of a control apparatus connected to the fluid return line for establishing or interrupting different flow paths of the measuring system, by means of a transducer apparatus for generating at least one electrical measurement signal corresponding to the at least one measured variable, an electrical measurement signal having at least one signal parameter dependent on the measured variable, or reacting to a change of the measured variable with a change of the signal parameter, as well as by means of a fluid withdrawal line.
The transducer apparatus—embodied in such case as a component of a vibronic measuring transducer serving for generating two measurement signals having a phase angle dependent on the mass flow rate and a signal frequency dependent on the density of the fluid—comprises a first tube and a second tube. The two tubes are connected permanently for parallel flow via an inlet-side line branch as well as an outlet-side line junction and are, in such case, additionally adapted to be flowed through simultaneously by fluid during operation of the measuring system and while such flow is occurring to be cause to vibrate for the purpose of generating the measurement signals.
The control apparatus—in such case formed by means of a check valve as a well as a return valve having two switch positions—is provided selectively to create a first flow path leading from the lumen of the fluid supply line to the lumen of the first tube of the transducer apparatus and, in parallel, to the lumen of the second tube of the transducer apparatus and further from the lumen of the first tube and from the lumen of the second tube, in each case, to the lumen of the fluid return line, equally as well not to the lumen of the fluid withdrawal line, in such a manner that, of fluid allowed to flow along the first flow path, a volume portion flows through the lumen of the first tube further to the lumen of the fluid withdrawal line and at the same time another volume portion flows through the lumen of the second tube further to the lumen of the fluid return line, or, selectively, a second flow path leading from the lumen of the fluid supply line to the lumen of the first tube of the transducer apparatus and, in parallel, to the lumen of the second tube of the transducer apparatus and further from the lumen of the first tube, and from the lumen of the second tube, in each case, to the lumen of the fluid withdrawal line, equally as a well not to the lumen of the fluid return line, in such a manner that of fluid allowed to flow along the second flow path a volume portion flows through the lumen of the first tube further to the lumen of the fluid withdrawal line and at the same time another volume portion flows through the lumen of the second tube further to the lumen of the fluid withdrawal line. The first flow path begins and ends, in each case, in the supply container and serves here especially as recirculation system for preventing impurities within a volume portion of the fluid ultimately to be filled via the second flow path into an appropriate withdrawal container, for example, a tank of a tank truck. For conveying fluid along the first flow path and along the second flow path, the measuring system includes, furthermore, a corresponding transport pump. Additionally, the measuring system comprises electrically coupled with the transducer apparatus a measuring- and operating electronics, which is adapted to process the at least one measurement signal, to ascertain by means of the at least one measurement signal the measured values for the at least one measured variable, as well as electrically coupled with the control apparatus a control electronics, which is adapted to deliver control signals operating the control apparatus, for example, control signals carrying control commands effecting the setting of the first flow path and the second flow path. The measuring- and operating electronics and the control electronics are components of one and the same device electronics of a conventional Coriolis mass flow measuring device or Coriolis mass flow/density measuring device formed together with the transducer apparatus and can accordingly also be accommodated in a single, shared, protective housing.
For filling a predetermined (or predeterminable) volume or a predetermined (or predeterminable) mass of fluid into the withdrawal container in the case of the measuring system shown in WO A 02/060805, the control apparatus, first of all, sets the transport pump in motion and thereafter opens the first flow path, so that, as a result, the fluid flows, first of all, from the supply container via the fluid supply line further through the tubes of the transducer system further to the fluid return line and from there back into the supply container. At the same time, the measuring- and operating electronics, based on the measurement signals generated concurrently by means of the transducer system, measures a density of the fluid flowing along the first flow path, in order to detect whether the fluid is composed of one or more phases, consequently in order to detect whether, or to what extent, the supplied fluid contains undesired impurities, or does not yet meet a relevant predetermined quality requirement or specification. If the measuring- and operating electronics detects, based on the measured density, that a single phase, or pure, fluid is flowing in the transducer system, consequently in the first flow path, this is correspondingly transmitted to the control electronics and then the control electronics outputs corresponding commands to the control apparatus, commands effecting the interrupting of the first flow path and the opening of the second flow path. Essentially at the same time, the measuring- and operating electronics, supplementally to measuring the density of the flowing fluid, starts measuring a (mass-) flow of fluid allowed to flow in the second flow path, in order so to ascertain an amount of the fluid allowed to flow via the second flow path, ultimately output via the fluid withdrawal line and correspondingly filled into the withdrawal container. A measuring system comparable as regards construction and operation of the above described measuring system, having both an openable first flow path as well as also a second flow path openable (alternatively) thereto, and serving for transferring fluid—in such case a cryogenic, consequently extremely cold, liquid is shown, for example, also in Published International Patent Application, WO A 2014/151829.
To be viewed as quite problematic in a conventional measuring system of the above indicated type is that the transducer apparatus and the control system are so embodied and arranged that downstream of the transducer apparatus components of the control system are arranged, in such case the return valve, which can act as a line branch for fluid flowing through the transducer apparatus actually in the direction of the fluid withdrawal line, with the consequence that, in the case of a possible, first of all, in given cases, also unrecognized, defect of the control system and/or the control electronics, the amount of fluid (evidently) measured by means of the transducer apparatus and the measuring—and operating electronics and allowed to flow along the second flow path can deviate significantly from the amount of the second fluid actually allowed to flow along the total second flow path, consequently along the fluid withdrawal line, and from the amount of fluid actually filled into the withdrawal container. Such a defect of the measuring system can be, for example, that a command for starting the measuring of the flow is produced erroneously by the measuring—and operating electronics or also by the control electronics, without that also corresponding commands, commands both opening the second flow path as well as also effecting interrupting the first flow path are output by the control electronics, or that the control electronics, indeed, correctly generates and outputs all commands for the control system, however, they are not immediately and/or not faultlessly performed by the control system, for instance, due to a defect of the return valve. An especially critical defect of the measuring system would be, for example, a not completely blocking return valve in one or both switch positions, consequently a return valve allowing leakage flow amounts of the fluid into the supposedly blocked flow path. Resulting therefrom, such measuring systems can, at times, also be rejected for use for traffic in goods where certification is obligatory or only be permitted after implementation of additional, costly measures for detection or reporting of the above referenced defects.